The present invention relates to a processing method using a focused ion beam and, more particularly, to a method for forming a three-dimensional pattern by etching using a focused ion beam.
Various etching methods are known as techniques for forming micropatterns on a specimen such as a silicon wafer in the manufacturing process of semiconductor devices. The etching method using an ion beam, in particular, is receiving a lot of attention. The ion beam method is classified, on the basis of the physical mechanism, into sputter etching, accelerated ion etching, ion beam assist etching, reactive ion etching and the like. A method is selected in accordance with the actual etching purpose.
FIGS. 1A and 1B are sectional views showing etching steps using sputter etching. As shown in FIG. 1A, after forming resist patterns 2 on a specimen 1 to be processed such as a silicon wafer, the structure is irradiated all at once with an Ar.sup.+ ion beam or the like having a relatively large and uniform spot diameter. Thus, using the resist patterns 2 as masks, processing regions 3 are formed by etching, as shown in FIG. 1B. Conventionally, desired regions are selectively etched in this manner by irradiation with an ion beam having a relatively large and uniform spot diameter.
However, the conventional method described above is subject to various drawbacks. Since the entire structure is irradiated all at one with an ion beam, the etching depth becomes uniform at all locations of the structure. For this reason, if etching to different depths is to be performed at selected regions, a plurality of etching steps and a plurality of masks are required, resulting in complex procedures. Furthermore, it is difficult to form patterns 4 and 5 of arbitrary cross-sectional shape, as shown in FIG. 2.